by Kim Hjelmgaard, USA TODAY

by Kim Hjelmgaard, USA TODAY

U.S. drug maker AbbVie has agreed to buy Shire Pharmaceuticals in a deal valued at nearly $55 billion, becoming the latest example of U.S. company seeking tax savings through a merger with a foreign partner.

AbbVie stock is down 1% premarket. Shire, based in Ireland and the British crown territory of the island of Jersey, is seeing its shares rise 1.8% in London trading.

The companies said Friday that Shire shareholders will receive cash and stock valued at about 53.19 pounds ($91.07) for each of their shares. They will control about 25% of a new company created as part of the deal. AbbVie shareholders will hold the remaining 75%.

The deal marks the latest U.S. drug firm to seek to shift its tax residence abroad -- a move known as a tax inversion -- in a record surge in industry deals in recent months. Forbes calls it the largest inversion deal ever.

Inversions have become increasingly controversial. Recent data from the Congressional Research Service shows 47 companies have done them in the past decade, many in the pharmaceuticals business. Treasury Secretary Jack Lew sent a letter to Congress this week calling for immediate action to close the tax loophole. There is a bill before Congress to tighten rules limiting inversions that would save $19.5 billion over 10 years, according to its Joint Committee on Taxation.

If the AbbVie-Shire deal closes, Chicago-based AbbVie's tax residence, though not its management, would move to the U.K.. The company's effective tax rate would drop to 13% by 2016 from 22% for 2013, according to regulatory filings.

Shire is headquartered in Dublin but incorporated on the island of Jersey for tax purposes. Tax rates are lower on the island, in the English Channel off the coast of France.